Circuit breaker



Sept. l, 1942. H. D. DoRFMAN CIRCUIT BREKER Filed May 15, 1941 2 Sheets-A-Sheet l insu] |NVENToR /v/z'Z/er 70W/(man.

Y q Y? Q/ATTOR WITNESSES:

H. D. DOR FMAN CIRCUIT BREAKER Sept. l, 1942.

Filed May l5. 1941 2 Sheets-Sheet 2 INVENToR #IIIe/. @0r/man WITN ESS ES:

Patented Sept. 1, 1942 UNITED STATES PATENT OFFICE Westinghouse Electric Manuiact pany, East Pittsburgh, Pa.. a corpo Pelililyl Comn of Animation may is, 194i. semi No. :93,535

(ci. zoo-11s) 18 Claims.

This invention relates to circuit breakers and more particularly to circuit breakers oi the type which are tripped instantaneously on overload currents above a predetermined value, and after a time 'delay on overloads below said predetermined value.

One object oi' the invention is to provide an improved circuit breaker oi the above type that is compact, safe fand reliable in operation. and which can be manufactured at low cost.

Another object oi the invention is to provide a multipole circuit breaker embodying an improved trip mechanism in which the main latch is moved to release the operating mechanism by any one of a plurality oi spring biased trip mem' bers each restrained in inoperative position in a novel manner by an individual bimetal element.

Another object oi' the invention is to provide an improved multi-pole circuit' breaker having a plurality oi trip members biased by springs to trip the breaker, and a plurality of bimetal elements each having a free end disposed in the path of movement oi its associated trip member at all times for opposing movement oi the trip member to tripping position.

Another object of the invention is to provide a multi-pole circuit breaker having a plurality ot tripping elements each independently movable to trip the breaker, an individual means for moving each tripplngelement to trip the breaker, and a plurality ofblmetal elements one for each trip element, each bimetal element being disposed to yieldingly oppose tripping movement oi' its corresponding trip element through substantially the entire range of tripplna movement.

Still another object oi the invention is the provision oi an improved multi-pole circuit breaker having atrip device comprising a bimetal ele-- ment and an electromagnetic trip means for each pole, each bimetal element being disposed to yieldingly oppose operation oi the corresponding magnetic trip means.

Another object of the invention is to provide a multi-pole circuit breaker having ka plurality of independently movable trip members each movable to trip the breaker by an individual overload electromagnet energized by current ci its corresponding pole, and a plurality of thermally responsive bimetal elements one for each trip member each yieldingly. opposing tripping movement of its corresponding trip member, the construction being such that any one electromagnet when operated has only to overcome the spring iorce oi the corresponding bimetal element to trip the breaker.

A further object of the invention is the provision of a multi-pole circuit breaker having a common operating mechanism and a trip device comprising a plurality of independently movable tripping members one for each pole each biased to move to a tripping position to' cause automatic opening of the breaker. and a separate current responsive bimetal element for each pole disposed to yieldingly oppose tripping movement of its corresponding trip member by the inherent resilience of the bimetal element and operable when heated' a predetermined amount by overload current to permit movement of its corresponding trip member to tripping position.

Another object of the invention is the provision of a circuit breaker as described in the preceding paragraphs wherein the tripping movement of4 any one of the .trip members is unopposed by the bimetal element of any ci the other poles.

Another object oi the invention is to provide a multi-pole circuit breaker having a common operating mechanism for the several poles, and a trip device comprising a plurality oi independently operable tripping members each operable to cause automatic operation of the breaker and each comprising a series overload electromagnet and a current responsive bimetal element which cooperates in a novel manner with the electromagnet to provide an improved automatic operating characteristic.

Another object of the invention is to provide a multi-pole circuit breaker having a plurality of trip members each or which members is biased to unlatching position land independently movable, each trip member being yieldingly restrained by a thermal element responsive to overload currents of its pole.

'lhe novel features that are considered characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to structure and operation, together with additional objects and advantages thereoi', will be best understood from the following detailed description of one embodiment thereof when read in conjunction with the accompanying drawings. in which:

Figure 1 is a top plan view of a three pole circuit breaker embodying the principles of the invention. a portion oi the cover being shown broken away to more clearly show-,.thestructure. y Fig. 2 is a sectional view oi' the circuit breaker taken substantially along the lineyI-II o! Pig. l, the breaker being shown in closed circuit position,

m. s is a sectiomu view stmusr to ma. 2. butl showing the circuit breaker in the tripped open position,

Fig. 4 is a perspective view of the trip device, and a portion of the circuit breaker operating mechanism, and,

Fig. 5 is a top plan view of the trip bar.

Referring to Figures l and 2 of the drawings, the circuit breaker includes a base of molded insulating material on which the several elements of the mechanism are mounted. The circuit breaker comprises three separate poles, each of which is provided with terminals I3 and I5 for connecting said poles in electrical circuits, a stationary contact i1, an arc extinguisher |9, a movable contact 2|, and a trip device indicated generally at 23. Each of the movable contacts 2| is mounted on the free end of a resilient contact arm 25 having its other end secured to a frame member 21. A flexible shunt conductor 29 connects the movable contact 2| with a conductor 3| which completes the electrical circuit from the shunt 29 to the trip device 23. A cover 24 of insulating material is provided and forms a part of the closure for the mechanism.

Each of the stationary contacts I1 is secured by means of a screw 33 to the formed over end of a conductor 35 which connects it to the terminal I5. The terminal I3, at the opposite end of the breaker from the terminal I5, is connected by a ilexible shunt conductor 31 to a point near the free end of an arcuate shaped thermally respon- 4sive element 39 of bimetallic material. The other end of the thermal element 39 is secured to the conductor 3| by a screw 4|.

Battles I9 are moulded integral with the base I I between the poles, and similar baiiies 26 moulded integral with the cover 24 cooperate to form a substantially separate chamber for each pole.

The electrical circuit for each of the poles is essentially the same and extends from the terminal I3 through the iiexible shunt 31, the thermal element 39, conductor 3|, ilexible shunt 29, contacts 2| and I1, and conductor 35 to the terminal I5.

The operating mechanism for the breaker is supported on a U-shaped frame 43 secured to the central portion of the base by means of screws 45. This mechanism includes a forked operating lever 41, toggle links 49 and 5|, a pair of overcenter springs 53 and a releasable cradle 55 controlled by the trip device 23. The cradle 55 is pivotally supported on the frame 41 by a pin 56. The operating handle 41 is pivotally supported on the frame 43 by pivot pins 51 and has secured to its outer end an insulating shield 59 for covering an opening 9| in the cover y24, through which opening extends a handle projection 99 of the shield to permit manual operation of the circuit breaker.

The toggle links 49 and 5| are pivotally connected by a knee pin 95. The link 5| is pivotally connected by a pivot pin 91 to the center pole frame member 21 which carries the central contact arm 25, and the link 49 carries a pin 99 which fits in a pivot bearing recess in the apex of the cradle 55 and is retained in the recess by the overcenter springs 53 tensioned between the knee pin 95 and the outer portion of the operating lever 41. The overcenter movement of the toggle 495I is limited by a stud 59 on the link 5| Just below the knee pin 95 striking a projection 99 on the cradle 55. This projection also acts to positively start the collapse of the toggle when the breaker is tripped automatically in response to an overload as will be described later.

The clockwise and counter-clockwise movements of the handle 41 are limited by odset proiections 1| and 13 respectively on the mechanism frame 43. The three contact arm frames 21 are rigidly connected together by an insulating tie bar 15 which is rigidly fastened to each o! the frames 21 by a strap 11., The assemblage of the contact arm frames 21 is pivotally mounted on the mechanism frame 43 by means oi a single pivot pin 19.

The trip device 23 (Fig. 2), as previously mentioned, includes three arcuate thermally responsive elements 39, there being an element 39 connected in series in the circuit of each pole of the breaker. The trip device also includes a trip bar 9| common to all three poles. The trip bar 9| is oi molded insulating material and is pivotally supported by means of an axially disposed rod 93 extending therethrough which is rotatably supported at each end by a pair of spaced brackets 95. These brackets, one being disposed at each end of the trip bar 9|, are supported on shoulders 91 molded in the base and are secured to the shoulders by means oi' screws 99. The trip bar 9| is provided with three arms 9| formed integral therewith and three trip members 93 are disposed one above each of the arms 9|. The free ends of the arms 9| carry projections 95 which extend into openings 91 in the trip members 93 to align the members. 'The right hand ends (Fig. 2) of the trip members are bent as indicated at 99 to engage notches |9| in the body of the trip bar 9|. Springs |93 compressed between a cross bar |95 supported on projections |91 of the baiiies I9 and the trip members 93, bias said members 93 against the trip bar 9| at one end and bias adjusting screws |09 at the opposite end o! the members 93 against the free ends of the thermal element 39. Lock nuts III are provided to retain the screws |99 in their adjusted positions., The ends of the springs |93 are seated around a piu. rality ot portions |29 stuck out from the trip members 93, the portions |29 acting as a spring seat.

A U-shaped latch member ||3, rigidly molded integral with the trip bar 9| normally engages the latch end of the cradle 55 and thereby restrains the operating mechanism against automatic circuit opening operation.

When any one oi the bimetal elements 39 is heated a predetermined amount by overload current, the free end thereof iiexes toward its nxed end. 'I'he corresponding trip member 93 follows under the iniluence of the spring |93 rocking the trip arms 9| and the trip bar 9| counter-clockwise as shown in Fig. 3. At this movement of the trip bar 9| the latch |I3 'releases the cradle 55 permitting the over-center springs 53 to actuate the operating mechanism and open the contacts as will be more fully described later.

The trip members 93 of the unaected poles remain in normal positions shown in Fig. 2 so that the spring |93 of the overloaded pole only has to overcome the latch friction to trip the breaker and does not have to compress the bimetal elements 39 oi the other poles. I

The trip device is also operated electromagnetically to instantaneously trip the breaker upon the occurrence of a heavy overload, for instance, 1000% or more of rated current or on short circuits in the circuit throughy any pole of the breaker. Each pole of the breaker is provided with an electromagnetic trip means comannesse prising a U-shaped core ||2 oi magnetic material and a cooperating amature |22. The core members ||2 are secured to the base by screws ||1. Yokes ||2 of non-magnetic material nt around the three core members ||2 and are retained in position by the screws ||1. The oonductors 2| for the three poles extend through the respective core members ||2 but are insulated therefrom by strips of insulating material |2|. The conductors 2| carry the entire current ilowing through the several poles and serve to energize the core members I |2.

The armatures |22 are mounted on the inner ends of rods |22 extending through yand guided by openings in the yokes ||2. At their outer ends the rods |22 extend through enlarged openings in the corresponding trip arms 2| of the trip bar 2| and also through openings in the trip members 22. Each rod |22 is provided with a nut |21 screwed on the outer end to provide a means whereby the pull of the core members ||2 is transmitted to the trip member 22.

A spring |22 surrounding the armature rod |22 associated with the center pole biases the trip arms 2| and the trip bar 2| to latching position. Only one spring |22 is provided and is compressed between the yoke ||2 and the trip arm 2| for the center pole. The yoke ||2 for the center pole is formed to provide an outwardly extending lip at the opening lor the rod |22 and acts as a seat or retainer for the spring |22. The other end oi the spring |22 is seated around a sleeve |2| suitably secured in the trip arm 2| for the center pole.

The screws |02 serve as convenient means for adjusting the tripping time od the breaker when tripped by the .blmetal elements 22 on overloads up to a predetermined value. approximately 1000% of normal rated current. The springs |22 maintain the screws |22 in contact with the free ends or their respective bimetal elements 22 at all times and the spring |22 biases the arms 2| oi the trip bar into contact with the trip members 22. Consequently ir the screws |22 are rotated to move them relative to the trip members 22 the result will be a corresponding movement of the trip members 22 and, due to the innuence ot springs |22 and |22, the trip bar 2| and the latch member ||2 will receive a similar movement to adjust the relationship of the latch member I2 with the cradle 22.

On overloads up to approximately 1000% of rated current the spring |22 assisted by the pull ot the electrounagnet (armature |22) associated with the pole in which the overload occurs has to overcome the force of the spring |22 and the spring iorce of the bimetal element 22 tor that pole only in tripping the breaker. The pull o! the electromagnet in the lower range of overload currents is very slight but increases as the magnitude of the overload increases, and becomes considerable in the higher value overloads even below approximately ten times rated current. Thus on lower overloads as the bimetal becomes heated-and bends inwardly, it is the spring |22 which provides the 'force lor rocking the trip member 22. trip bar 2| and the latch member ||2 to trip the On higher overloads below the predetermined value. the spring |22 is assisted by the pull oi the electromagnet but since the force of the armature is against the bimetal elements 22 until it has become heated. a desirable but shorter time delay is eilected.

The forces exerted to trip the breaker are exerted only against the bimetal element 22 associated with the particular pole in which the overloadoocurs since the trip anus 2| and the trip bar 2| are operable" independently ol.' the trip members 22 o! the other poles.

When. a heavy overload above the predetermined value or a short circuit occurs in any one ot the poles. the corresponding electromagnetic trip means is strongly energized and attracts its movable armature |22. This' movement, throughtheagencyodtherod |22 andthenut |21, rocks the trip member 22 for that particular pole and the trip bar 2| counterclockwise. The force exerted by the electromagnet on such overloads is sumcient to overcome the inherent resiliency o( the bimetal element 22 and the spring |22 ami tc rock the trip bar 2| to trip the cradle 22 substantially instantaneously.

I'he circuit breaker mechanism is shown in Fig. 2 in the closed circuit position with the trip device in untripped position. When the trip bar 2| is rocked in unlatching direction in response to an overload in the circuit through amr one oi the poles, the latch member |l2 disengages the cradle 22 and `permits that member to rotate clockwise about its pivot 22 under the iniluence of the overcenter springs 22. At the start oi' this rotation oi' the cradle 22 the projection 22 engages the stud 22 and starts the toggle 22-'2i in a direction to cause collapse thereof. Continued movement of the cradle 22 carries the center line oi the toggle link 22 to the right of the line oi action ol the springs 22 which act to complete the collapse o! the toggle. This rocks the trame 21 counter-clockwise and opens the contacts in all o! the poles. Automatic opening of the contacts will take place irrespective of the position o! the operating lever 21. The operating lever 21 is also automatically moved to an intermediate indicating position as shown in Fig. 3 upon tripping of the circuit breaker.

Following each opening oi' the circuit due to an operation of the trip device, it is necessary to reset the operating mechanism ltoan operative condition before the circuit breaker can be reclosed. As the bimetal 32 cools following a tripping operation in response to an overload below a predetermined value it resumes its normal position (Fig. 2) rocking the trip membex 22 clockwise against the force of the spring |22. When this occurs the spring |22 also rocksgthe trip arm 2| and the trip bar 2| in the same direction to the operative position shown in Fig.

2. To reset the mechanism, the lever 21 is rotated from the position in which it appears in Fig. 3 to its extreme counter-clockwise or open position. This movement of the lever l21 is transmitted to the cradle 22 by means o! a hook projection |22 which engages a portion |22 crt the cradle 22 and rocks the cradle counter-clockwise therewith. As the cradle 22 is rotated the end thereof passes the latch member III and engages'a pin |21 mounted between a pair of spaced arms |22 i'ormed integral with the trip bar 2|. The pin |21 limits the counter-clockwise movement of the cradle 22. y

After the cradle 22 has been relatched the contacts may be closed manually by moving the handle 22 clockwise to its closed circuit position. As soon as-the line of action of the overcenter springs 22 crosses to the right oi' the pivot axis 22 o! the toggle link 22, said springs cause the toggle 22-2| to move to the overcenter position wise direction about its pivot 51. This movement carries the line of action of the springs Il to the leit oi' the pivot axis 69 od toggle link Il and the force exerted by the springs 53 now .biases the toggle 49-5I away from its overcenter position. Before the handle 'reaches its extreme counter-clockwise position, this force becomes suiliciently great to cause the toggle to collapse. Since the toggle link 5| is pivotally connected to the central contact arm frame member 21, this member is rotated in a counter-clockwise direction about its pivot 'I9 causing opening of the contacts with a snap action. The contacts are closed manually in the previously described manner.

The circuit breaker is entirely trip free, that is, it operates in response to an overload to open the contacts regardless of the position of the operating lever 41.

The arc extinguishers I9, there being one provided for each pole, are of the spaced plate type and comprise, generally, a stack of slotted plates of magnetic material positioned adjacent the path of movement of the contacts. The presence of these plates causes the arc to move in the direction toward the ends of the slots which results in the breaking up of the arc into a plurality `of short arcs and causes cooling and extinguishment of the short arcs.

Having described the preferred embodiment of the invention in accordance with the patent statutes, it is to be understood lhat various changes and modifications may be made in the particular embodiment disclosed without departing from some of the essential features oi the invention. It is, therefore, desired that the invention be interpreted as broadly as possible in view of the prior art, and that it be limited only lby what is expressly stated in the following claims.

I claim as my invention:

l. In a multi-pole circuit breaker, the combination with a spring biased actuating member releasable to eiiect circuit opening operation oi.' the breaker, of a trip device including a trip bar common to all of the poles of the breaker, said bar being biased to latching position, a latch for restraining the actuating member in inoperative position, said latch being operable by the trip barl to unlatch the actuating member, a plurality of trip members operatively associated with the trip bar, said trip members being biased to operate the trip bar, and a plu rality of thermal elements each having a free end disposed in the path of movement oi.' a corresponding one of the trip members at all times for opposing movement of said trip member to tripping position, said thermal elements being responsive to predetermined circuit conditions in the circuit of their associated poles to independently cause movement oi the trip bar to unlatch the actuating member.

2. In a multi-pole circuit breaker, a plurality of pairs oi relatively movable contacts forming a plurality of poles, an operating mechanism for opening and closing the contacts, a latch member operable to cause operation of said mechanism, a trip device including a common trip bar for operating the latch member, said trip bar being based toglatching position, a plurality oi independently movable trip members for causing operation of the trip bar, said trip members being biased to tripping position, and a thermal element connected in the circuit of each pole, said elements 'actingv to yieldingly oppose move'- ment oi the trip members to tripping position, each thermal element being responsive to predetermined circuit conditions in its corresponding pole to cause tripping movement ot its assoelated trip member independently of the remaining thermal elements, said trip member remaining in engagement with the thermal element during substantially its entire movement.

3. In a multi-pole circuit breaker, a pair of relatively movable contacts for each pole, operating mechanism i'or substantially simultaneously opening and Aclosing said pairs o! contacts, a common trip bar including a latch member. said bar being operable to cause operation of the operating mechanism, a plurality of trip members, one associated with each of a plurality of the poles, said trip members being individually biased to operate the trip bar, a plurality o! thermal elements, one operatively associated with each trip member to normally restrain the` trip members in inoperative position, said thermal elements being responsive to overload currents below a predetermined value in their respective poles to cause operation of the trip members, and a plurality of electromagnets, one for each of a plurality oi' the poles, said magnets being responsive to overload currents above s predetermined value in their respective poles to operate the trip members.

4. In a multi-pole circuit breaker, relatively movable contacts for each pole, an operating mechanism for said contacts, s trip bar common to at least two of the poles, said trip bar being operable to cause circuit opening operation of the mechanism, a trip member for each of at least two poles of the breaker operable to operate said trip bar, and a thermal element i'or each trip member having a free end disposed in the path oi' movement oi its trip member at all times for opposing movement of the trip member to tripping position, said thermal element being responsive to predetermined circuit conditions to cause operation of the trip member.

5. In a circuit breaker, the combination of e. spring biased actuating member releasable to eiIect opening of the circuit, a trip device including a releasable latch means for restraining the actuating member in inoperative position, a pivoted trip bar movable from a normal position to a second position to release the latch means, a trip member movable relative to the trip bar and operable to cause operation of the trip bar, a thermal element yieldingly restraining the trip member in inoperative position, said thermal element being responsive to overload currents below a predetermined value to cause operation of said trip member, and an electromagnet operable to operate the trip member.

6. In a circuit breaker, the combination of a spring biased actuating member releasable to cause opening of the circuit, a trip bar including a latch member for restraining the actuating member in inoperative position, said trip bar being biased to latching position, a thermal element heated in response to the current oi.' the circuit, a trip member having one end engageable with the trip bar, said trip member being biased to move the trip bar to release the actuating member, said thermal element yieldingly opposing movement of the trip member to tripping position at all times and being responsive to predetermined circuit conditions to cause the trip member to operate the trip bar to release the actuating member, and an electromagnet" operable to move the trip member to trip the breaker.

7. In a circuit breaker, the combination of an actuating memberl releasable to cause circuit opening operation of the breaker, a trip bar including a latch member for restraining the actu-v ating member in inoperative position, a bimetal element in the circuit of the breaker, and a trip member operable to operate the trip bar, said trip member having one end biased against the fiat side of the bimetal element adjacent the free end of said element, said bimetal element acting to yieldingly restrain movement of the trip member to tripping position and being responsive to predetermined circuit conditions to cause the trip member to operate the trip bar.

8. In a circuit breaker, relatively movable contacts. operating mechanism therefor, a trip bar operable to cause circuit opening operation of said mechanism, a bimetal element in the circuit of the breaker, a trip member biased to operate the trip bar, one end of said trip member engaging the fiat side of the bimetal element adjacent the free end of said element, said bimetal being responsive to overload currents below a predetermined value to cause the trip member to operate the trip bar, an electromagnet having an armature operatively connected to the trip member for operating the trip member, movement of the armature being yieldingly opposed by the bimetal element, said electromagnet being operable to cause the armature to operate the ytrip member.

9. In a multi-pole circuit breaker, the combination of relatively movable contacts, operating mechanism including a member releasable to cause automatic opening of the contacts, a trip d'evice including a latch member for restraining the releasable member, said trip device being provided with a plurality of arms and having a latching position, plurality of trip members cooperating with said arms, each trip member being individually movable and biased to operate the trip device, a plurality of bimetal elements, one for each of a plurality of the poles, yieldingly opposing movement of the trip members, said bimetalelements each being responsive to predetermined circuit conditions in its associated pole to cause tripping of the breaker, the trip members remaining in engagement with the bimetal elements during movement to tripped position.

10. In a, multipole circuit breaker, the combination oi actuating mechanism movable to cause opening of the breaker, a trip bar for effecting movement of the actuating mechanism, said trip bar being provided with a. plurality of arms and being biased to a normal position, a plurality of trip members each being individually movable and biased to engage a corresponding arm of the trip bar and to operate the trip bar to a tripped position, a bimetal element associated with each pole for yieldingly restraining its corresponding trip member in inoperative position, and a plurality of electromagnets responsive to overload currents and each having an armature operatively connected to one of the trip members, said bimetal elements yieldingly opposing movement of the armatures and being responsive to overload currents below a predetermined value to cause the trip members to reduce the air gap of the electromagnets and cause tripping of the breaker.

l1. In a circuit breaker, the combination of a spring biased actuating means releasable to cause opening of the breaker, a trip device including a latch member for normally restraining the actuating means in inoperative position, a trip bar having a normal position and operable io'eiiect unlatching of the actuating means, a trip member biased to operate the trip bar, electromagnetic means connected to the trip member and responsive to overload currents above a predetermined value to substantially instantaneously operate the trip bar, and a thermal element resiliently restraining the trip member in inoperative position, said thermal element being responsive to overload currents below said predetermined value to permit movement of the trip member to cause reduction of the magnetic air gap o! the electromagnet and permit said electromagnet to effect unlatching of the actuating means.

l2. In a multi-pole circuit breaker the combination of an operating mechanism releasable to cause simultaneous-opening of the circuits of all of the poles of the breaker, a trip bar extending across at least two poles of the breaker, a latch member on said trip bar for releasably restraining the operating mechanism, a plurality of bimetal elements, one for each polel a. plurality of trip members, each being independently movable and biased to operate the trip bar, said trip bar having a plurality of arms engageable by the trip members and opposing unlatching operation of said members, each of the bimetal elements being responsive to overload currents below a Predetermined value in the circuit of its associated pole to cause operation of the corresponding trip member independently oi' the other trip members to unlatch the operating mechanism and an electromagnetic means operatively connected to each trip member. and responsive to overload currents above said predetermined value to operate said trip member.

13. A trip device for a multi-pole circuit breaker comprising a trip bar operable to cause opening of the breaker, a plurality of independently movable trip members one for each pole each biased to operate the trip bar, a thermal element for each trip member yieldingly holding the trip member against tripping movement, and an electromagnetic means for each trip member operable to cause tripping movement thereof.

14. A trip device for a multi-pole circuit breaker including releasable operating mechanism for causing simultaneous opening of the circuits of all of the poles, said trip device comprising a latch member for restraining the operating mechanism, said latch member having a latching position and being movable to a tripped position, a plurality of trip members independently operable to cause unlatching of the operating mechanism, individual means for biasing the trip members to unlatching position, a plurality of thermally responsive elements, one for each 'trip member for yieldingly holding said trip members against movement to tripping position, and a plurality of electromagnets, one for each pole, for operating the trip members in response to predetermined circuit conditions.

l5. In a multi-pole circuit breaker, the combination of an operating mechanism for the several poles and a trip device comprising a plurality of individulally movable tripping members, each member being movable to a tripping position to cause automatic operation of the breaker, a separate series overload electromagnet for each of a plurality of the poles acting to move the corresponding trip member to tripping position, and a separate current responsive bimetal element for each pole disposed in cantilever manner to yieldingly oppose tripping movement of its corresponding trip member, each bimetal element being operable in response to predetermined overload conditions to permit tripping operation of its corresponding trip member.

16. In a muilti-pole circuit breaker, the combination of an operating mechanism for the several poles, and trip device comprising a plurality or independently movable tripping members biased to move to a tripping position to cause automatic openinug of all. of the poles of the breaker, and a separate current responsive bimetal element for each of a plurality of poles disposed to yieldingly oppose tripping movement of its corresponding trip member by the inherent resiliency of the bimetal element and operable when heated a predetermined amount by overload current to permit movement of its corresponding trip member to tripping position.

17. In a multi-pole circuit breaker, the combination of an operating mechanism and a trip bar extending across at least two poles of the breaker and operable to trip the breaker, a plurality ot independently movable tripping members each biased to move to tripping position to operate the trip bar to trip the breaker, and a separate current responsive bimetal element for each pole disposed in cantilever manner to yieldingly oppose tripping movement of its corresponding trip member, the tripping movement of any one of the tripping members being unopposed by the bimetal elements of any of the other poles.

18. In a multi-pole circuit breaker, operating mechanism for the several poles, a. trip member movable to cause the operating mechanism to open all of the poles, a plurality of bimetaliic members, each responsive to the current through one pole and operable to cause actuation oi' the trip member, a plurality of electromagnets, each responsive to the current through one pole and operable to cause actuation oi the trip member, and each ot said bimetallic members being connected to one of said electromagnets to vary the tripping point of the electromagnet as the bimetallic member is moved in response to current.

KILLER D. DORF'MAN. 

